In transmitters, in order to suppress non-linear distortion caused by the amplifier, digital pre-distortion (DPD) is performed for correcting transmission signals using distortion correction coefficients. In the DPD, digital sound signals are multiplied by a distortion correction vector stored in a look-up table (LUT), the distortion correction vector corresponding to the amplitude of the digital sound signals.
The orthogonal frequency-division multiplexing (OFDM) modulator disclosed in Unexamined Japanese Patent Application Kokai Publication No. 2011-188093 extracts, for each given sample, an error signal that is an error between a baseband signal corresponding to an input signal and a feedback signal from an amplifier, calculates the average values of error signals, and interpolates between the average values. The OFDM modulator estimates a distortion based on the interpolated average values of error signals and creates data for distortion compensation from the distortion.
The non-linear distortion compensation transmission device disclosed in Unexamined Japanese Patent Application Kokai Publication No. 2004-343594 compares input signals with output signals of an analog-to-digital (A-D) converter and detects distortion components that are the differences. For updating the compensation data for offsetting the non-linear distortion components, the approximate calculation interval is shifted, function approximation is performed on the compensation data in the shifted approximate calculation interval, and the compensation data are updated.
In order to reduce the time to calculate distortion correction values, the radio device disclosed in Unexamined Japanese Patent Application Kokai Publication No. H08-079143 compares output of a transmitting amplifier with input signals entered into the transmitter to output the quantity of distortion of the transmitting amplifier that should be corrected, and further obtains distortion correction values at a time by interpolation using the quantity of distortion. The output distortion occurring in the transmitting amplifier is corrected by preliminarily correcting modulation signals with the distortion correction values and entering the modulation signals into the transmitting amplifier.